challtestsrv.py: change address of target (#6234)
challtestsrv.py: change address of target (#6234)

Previously challtestsrv.py (used by chisel.py) assumed challtestsrv runs
on localhost. But we can also reach it on the fixed IP 10.77.77.77, and
this allows running chisel2.py from the host in addition to running it
inside a container.
letsencrypt/boulder,letsencrypt/boulder,letsencrypt/boulder